The present invention relates to a positioning system for use in a numerical control apparatus, a robot control apparatus, or the like. More particularly, the present invention is directed to a positioning system which uses a feedback signal as a positional information signal to effect a highly accurate and high-speed positioning operation.
Conventional positioning systems have employed a pulse train having a certain weight, e.g., a pulse corresponding to, for example, 1 .mu.m, or any other predetermined time period, as a feedback signal. One example of such an arrangement is shown in FIG. 3 of the accompanying drawings. Denoted in FIG. 3 at 1 is a pulse distributor for generating distribution pulses in response to a tape input or the like, 2 a command processor for comparing pulses from the pulse distributor 1 and feedback pulses and issuing a servo command signal, 3 a servoamplifier responsive to the servo command signal from the command processor 2 for driving a servomotor 4 to actuate a movable unit (not shown. The servomotor 4 includes an encoder 5 as a position detector coupled to the shaft of the servomotor 4 for generating feedback pulses 8 as a feedback signal, and an up/down counter 7 for counting the feedback pulses 8. The count is read by the command processor 2.
For a numerical control apparatus and the like, there are demands for higher positioning accuracy and higher pulse distribution rate. The conventional systems have difficulty in meeting such demands.
More specifically, the pulse distribution rate of conventional systems is on the order of 1 MHz because of the characteristics of the transmission path for feedback pulses. The rate of the resolution "0.1 micron/pulse" at the pulse distribution rate is given by: ##EQU1## 0.1.times.10.sup.-6 indicates a numerical value representing "0.1 micron/pulse" in terms of meters (m), 10.sup.6 indicates the transmission rate for feedback pulses (1 MHz expressed by pps), and 60 indicates a numerical value for conversion to a value per minute. From the above equation, the speed of movement of the movable unit is 6 m/minute, indicating that a sufficiently high speed cannot be obtained.